The invention relates to an apparatus for absorption of impact energy acting on an element from at least one blade fragment, where the element is inserted into an opening in a turbo-machine which passes radially through a housing section in the region of a row of rotor blades, a turbo-machine having such an apparatus as well as a method for absorption of an impact energy acting on an element from at least one blade fragment, where the element is inserted into an opening in a turbo-machine which passes radially through a housing section in the region of a row of blades.
Turbine housings of high-speed turbo-machines such as gas turbines and aircraft engines in particular traditionally have very thick walls to retain the blade and/or the blade fragment in the interior of the turbine after loss of a blade or loss of a blade fragment. Therefore, to prevent weakening of the turbine housing and/or to achieve so-called “containment capability” of the turbine housing, holes and/or openings in the turbine housing in the region of the rotor blades are generally avoided. However, if apparatuses for clearance maintenance and/or for measuring the clearance of a radial clearance between a row of blades and a housing section surrounding the rotor blades are provided, then openings for positioning appropriate elements such as sensors, probes and the like are unavoidable. In impact with such a rigid element, the kinetic energy of the blade and/or of the blade fragment is transferred completely to the element, which in turn delivers the energy to its attachment on the housing end. However, the high-energy density leads to an uncontrolled failure of the element mount and thus to release of the element from the housing section, which in turn results in loss of this “containment capability.”
U.S. Pat. No. 5,203,673 A discloses a tip clearance apparatus for maintaining the blade tip clearance for a turbo-machine, i.e., for maintaining a radial clearance between a rotor stage of a turbo-machine with rotor blades of a row of rotor blades of the rotor stage having a conical tip and a conical housing section surrounding the row of blades. The housing section is axially displaceable so that the radial clearance may be increased or decreased by an axial displacement due to the conical design. To detect the radial clearance and to control an actuator, at least one sensor which is permanently inserted into a radial opening is provided in the housing section. At least the one sensor is flush with the housing section near the clearance.
EP 1 754 861 A2 discloses an apparatus for detecting a radial clearance between a row of rotating blades of a rotor stage and a housing section surrounding the row of blades. This apparatus has at least one sensor, which is inserted into an opening on the housing and is set back in the opening on the clearance end with respect to the housing section. The sensor is secured in an insert which is bolted to the housing section directly or indirectly.
U.S. Patent Application Publication No. 2010/0313404 A1 also describes an apparatus for maintaining a radial clearance between a row of rotating blades of a rotor stage and a housing section surrounding that row of blades. The apparatus has a pressure-based actuator by means of which the housing section can be moved inward and outward radially.
EP 1 073 828 A1 discloses an apparatus for absorption of impact energy of a rotating blade and/or a rotating blade fragment of a turbo-machine. This apparatus has a ring system surrounding the row of rotating blades and consisting of a rigid outer ring and a plastically deformable inner ring. A deformation sheet is arranged between the rings. On impact, the internal ring undergoes deformation and releases its deformation energy at least in part to the deformation sheet. The rigid outer ring holds the inner ring and the deformation sheet in position.
The object of the present invention is to create an apparatus and a method by means of which a containment capability of a housing of a turbo-machine can be preserved in the event of an impact of at least one blade fragment with an element arranged on the housing end opposite a row of rotating blades. Furthermore, the object of the present invention is to create a turbo-machine having a high containment capability.
An apparatus according to the invention for absorption of an impact energy from at least one blade fragment acting on an element includes a holder for holding the element in an ideal position and which releases the element beyond a preset maximum load and a rear cage for securing the element in the event of a displacement acting radially outward. This element is inserted into an opening in a turbo-machine, the opening passing through a housing section in the region of a row of rotating blades.
The apparatus according to the invention permits dissipation of the impact energy in the region of an opening and thus in the housing region that is critical for containment. Due to the fact that the element is installed in a cage, so that it is movable in the radial direction, any energy input to the element is reduced in combination with the holder, which opens when the maximum load is exceeded. The cage secures the element on and/or in the region of the housing section, thus fundamentally preventing the element from being released from the housing section.
The maximum load on the holder can be adjusted and/or preset accurately if the holder has at least one intended breaking point.
The cage preferably limits the displacement space which is closed off with respect to the housing environment and/or the external environment. This prevents a substream of a primary flow that is flowing through the turbo-machine from emerging into the external environment through the opening in the event of such an impact. Furthermore, this also prevents blade fragments or element fragments from emerging through the opening into the external environment.
To preset the maximum displacement distance, the cage has a rear limit to act as a stop for the element so that the energy acting on the element can be further dissipated.
A turbo-machine according to the invention has at least one apparatus according to the invention and is therefore characterized in this way by a high containment capability. The turbo-machine is preferably a gas turbine and in particular is an aircraft engine.
If the element penetrates through the opening for a section and thus protrudes radially beyond the opening with a section on the inside, it is advantageous if the element in the cage is displaceable by a radial distance which is greater than the amount by which the element protrudes radially out of the opening on the inside. This measure ensures that the element can be completely driven into the opening and/or by the impact.
To keep the element in the opening after the impact, it is advantageous if the element is accommodated in its ideal position with a section in the opening, the extent of which is greater in the axial direction than the displacement distance. Holding the element with a section in the opening results in a sealing of the displacement space, thereby preventing penetration of a substream of the primary flow even after the impact. In an alternative exemplary embodiment, the axial extent of the section accommodated in the opening is smaller than or equal to the displacement distance.
The cage with a circumferential wall is preferably spaced laterally a distance away from the element. This prevents tilting of the element in the cage during displacement and thus ensures that the element will be shifted completely back into the opening, for example, in the case when the element protrudes with a section radially inward through the opening.
Assembly, disassembly and maintenance of the element and its holder can be simplified if the cage is detachably attached to a supporting section which surrounds the opening by a fastening section.
The ideal position of the element can be determined accurately if the element has a flange for contact with the supporting section in the axial direction of the element. The holder preferably attaches the element to the supporting section. In particular the element is pressed by the holder radially against the supporting section. Such a holder can also be implemented in a technically simple manner. Other holders are of course also conceivable such as, for example, locking rings which are inserted into circumferential grooves on the element and the supporting section and which release the element when the maximum load is exceeded.
In the case of a method according to the invention for absorption of an impact energy acting on an element from at least one blade fragment, where the element is inserted into an opening in a turbo-machine, which passes radially through a housing section in the region of a row of rotating blades, a first partial energy amount is absorbed by the element on impact of the at least one blade fragment, and when a predetermined maximum load is exceeded, a second partial energy amount is absorbed by a radial movement of the element outward and/or by running onto a rear limitation.
The method according to the invention guarantees preservation of the containment capability of the housing section and thus of the turbo-machine in the event of loss of a blade and/or loss of a blade fragment. A residual amount of energy is absorbed due to impact of the at least one blade fragment on a region of the housing section. The size of the energy input into the element depends on the ratio of the masses between the at least one blade fragment and the element, among other things. The lower the mass of the element in comparison with that of the at least one blade fragment, the lower is the amount of energy introduced into the element. The amount of energy introduced is reduced when friction losses are taken into account or when an impact having a plastifying component is assumed. An ideal elastic impact is the most conservative case. When a certain amount of energy introduced into the element falls below the expected threshold and/or when the maximum load on the holder is not reached, the load being adjustable through the mass ratios of the impact parameters, the impact no longer results in destruction of the holder.
Other advantageous exemplary embodiments of the invention are the subject matter of additional dependent claims. Preferred exemplary embodiments of the invention are explained in greater detail below with reference to a greatly simplified schematic diagram.